Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r262869:

ext2fs: Fix a bug when sorting htree entries.

This a typo introduced when bringing the original code from NetBSD.

Reported by: Mike Ma

MFC r262623, r262667:

ext2fs: use of tab vs spaces.

Consistently use a single tab after a #define as mentioned in style(9).
Use tabs instead of space for indenting.
Fix a typo: "hash_vesion".

No functional change.

MFC r260988, r261034, r261120, r261235:

ext2fs: Properly the EXT4_EXTENTS and EXT4_INDEX to the inode flags.

In order to support Ext4 extents we need to pass the Ext4 inode flags
without interfering with the chflags. This is better done by using the
i_flag field in the inode and doing proper translation to the linux
ext4 equivalents.

Solve a potential corruption issue in the dirindex code. The dirindex
code can now be renabled as the problems related to it have been
solved.

Suggested by: bde
Tested by: kevlo

MFC r255338:

ext2fs: temporarily disable htree directory index.

In addition to our implementation not having workarounds for hash
collisions, it appears we also have a compatibility problem.

For now disable the htree code until we are able to re-examine
both issues.

PR: kern/183230

MFC r252890, 252906, r252907, r253861, r254104:

Implementation of the HTree directory index.

This is a port of NetBSD's GSoC 2012 Ext3 HTree directory indexing
by Vyacheslav Matyushin. It was cleaned up and enhanced for FreeBSD
by Zheng Liu (lz@).

This is an excellent example of work shared among different projects:
Vyacheslav was able to look at an early prototype from Zheng Liu who
was also able to check the code from Haiku (with permission).

As in linux, the feature is not available by default and must be
enabled explicitly with tune2fs. We still do not support the
workarounds required in readdir for NFS.

Submitted by: Zheng Liu
Tested by: Mike Ma
Sponsored by: Google Inc.

Initial implementation of the HTree directory index.

This is a port of NetBSD's GSoC 2012 Ext3 HTree directory indexing
by Vyacheslav Matyushin. It was cleaned up and enhanced for FreeBSD
by Zheng Liu (lz@).

This is an excellent example of work shared among different projects:
Vyacheslav was able to look at an early prototype from Zheng Liu who
was also able to check the code from Haiku (with permission).

As in linux, the feature is not available by default and must be
enabled explicitly with tune2fs. We still do not support the
workarounds required in readdir for NFS.

Submitted by: Zheng Liu
Tested by: Mike Ma
Sponsored by: Google Inc.
MFC after: 1 week